The present invention relates to a magnetic head for video tape recorders having a pair of core tips, and more particularly to an improvement for limiting a quantity of sinking of a magnetic tape at a gap between both the core tips and reducing a noise in a special reproducing operation.
FIG. 6 is a plan view of a conventional magnetic head for a video tape recorder. The magnetic head includes a substantially square mounting base 1, a pair of projections 1A formed at one end of the mounting base 1, a central slit 2 formed between the projections 1A, and a pair of rectangular core tips 3 fixed at ends of the projections 1A and arranged in a spaced and symmetrical relationship to each other.
Each of the core tips 3 is formed at its end with a tape sliding surface 3A which is configured arcuately as viewed in plan the figure. The tape sliding surface 3A is chamfered at its opposite ends. In the prior art, a radius of curvature of each tape sliding surface 3A and a distance between both the tape sliding surfaces 3A are not precisely controlled. For instance, the radius of curvature is about 7-14 mm and the distance is about 0.05--0.6 mm in the prior art magnetic head for video tape recorders which are commercially available.
The mounting base 1 is formed with a central mounting hole 4 for mounting the magnetic head to a rotating drum of a video tape recorder. A magnetic tape is wound around the rotating drum in operation and is traveled thereby. Thus, the magnetic head operates to scan a recording surface of the magnetic tape during traveling to thereby record and reproduce a signal.
In a general video tape recorder for the people's livelihood, a tension to be applied to the magnetic tape during traveling of the tape in a special reproducing operation such as a video search operation is smaller than that in a normal reproducing operation. In the prior art magnetic head for a video tape recorder, a quantity of sinking of the tape at the gap between the core tips 3 in the special reproducing operation is unstable. Particularly, on the forward side of rotation of the rotating drum where the tension to be applied to the tape is especially small, a contact pressure between the tape and each core tip 3 is insufficient. As a result, there is generated transformation of a reproduced waveform of a single scan at its front end, causing the generation of noise and a reduction in visibility of images.
FIG. 7 shows such a waveform transformation of a reproduced signal as observed by using an oscilloscope. That is, after recording an electrical signal having a fixed amplitude and continuing for 1/60 seconds generated by a signal generator onto a magnetic tape with use of a video tape recorder unit employing the prior art magnetic head, the recorded signal is reproduced in a reverse video search operation with use of the same video tape recorder unit, and a reproduced signal obtained is observed by using the oscilloscope. As apparent from FIG. 7, the waveform transformation is generated at a front end F of the waveform.